As a conventional type of coordinate-position detecting device, there is one, for instance, comprising two light sources each for irradiating light in parallel with a display surface of a display unit while rotating. Reflecting sections are provided each for recursively reflecting the light from the light source in its incident direction, and detecting sections are provided at positions where the light sources are provided respectively each for receiving the reflected light from the reflecting section.
The two light sources irradiate, while changing the direction, light to the reflecting sections in parallel with the display surface of the display unit. Each of the reflecting sections recursively reflects the light to the light source. Each of the detecting sections provided at the position of the light source receives the light recursively reflected from the reflecting section. When the light is blocked by a finger or a pen, the detecting section detects the direction of the light source. Coordinates of the position indicated by the finger or the pen can be computed from a distance between the two light sources and the detected directions of the two light sources.
FIG. 16 is a general view of a coordinate-position detecting devices based on the conventional technology. The conventional type of coordinate-position detecting device shown in FIG. 16 comprises a display unit 1601 having a rectangular display surface as a coordinate-position input area. Reflecting members 1602A, 1602B, and 1602C are provided each for recursively reflecting an incident light back to the light source. Light scanners 1603A and 1603B are provided for irradiating a light beam while rotating and receiving the light reflected by any of the reflecting members. A computing section 1604 computes the coordinates indicated by a pen 1607 used for entering a coordinate position, and an interface 1605 outputs the coordinates of the pen 1607 computed by the computing section 1604.
Each of the reflecting members 1602A, 1602B, and 1602C is constructed with a corner cube array where a number of corner cube reflectors are arranged or a recursive reflecting tape, and its reflecting surface is a rectangle. The reflecting members 1602A, 1602B, and 1602C are provided on right, left and lower side of the display unit 1601 so that each of the reflecting surfaces is perpendicular with respect to the display surface of the display unit 1601.
The light scanners 1603A and 1603B are provided above the display unit 1601 at both edges thereof respectively. The light scanners 1603A and 1603B irradiate light to the reflecting members 1602A, 1602B, and 1602C while changing their directions, and receive the reflected light from the reflecting members 1602A, 1602B, and 1602C. When the light is blocked by the pen 1607, the light scanners 1603A and 1603B detect that the light is blocked, and detect the angles .theta.3 and .theta.4 corresponding to the directions of the light scanners 1603A and 1603B at that point of time.
The computing section 1604 obtains the angles .theta.3 and .theta.4 from the light scanners 1603A and 1603B respectively, computes the coordinates (X2, Y2) indicated by the pen 1607 from the previously measured and inputted distance W2 between the light scanners and the angles .theta.3 and .theta.4, and sends the coordinates (X2, Y2) to a personal computer PC or the like through the interface 1605.
In the coordinate-position detecting device having the reflecting member described above, when there is a foreign substance, dust or dirt (which will be collectively called as dirt) on the reflecting surface of a reflecting member, a light beam is blocked by this dirt and does not reach the reflecting surface or can not by reflected thereby. Therefore there occurs a malfunction such that it is determined as if an instruction is given by a pen on a display surface or the like despite there is no instruction given by a pen.
Especially, in the coordinate-position detecting device having light scanners provided above the display unit at both edges thereof and having reflecting members provided on right, left and lower side of the display unit, dirt is easily deposited on the reflecting surface of the reflecting member located in the lower side of the display unit which is facing in an opposite directed with respect to the direction of gravity. Further, when a white board is used in place of the display unit and something is written on it with a marker pen, dirt generated when the writing with the marker pen thereon is erased drops onto the reflecting surface of the reflecting member located in the lower side of the white board and blocks the light, which may again cause malfunction.
When the user notices the malfunction or notices that dirt is deposited on the reflecting surface of a reflecting member, he or she removes the dirt by cleaning such as wiping with a cloth in order to avoid the malfunction and then restarts using the board.
In the conventional technology, cleaning is carried out as necessary when dirt is deposited on the reflecting surface of a reflecting member. However, the deposited dirt may be a cause of malfunction because it is easy for the dirt to get deposited on the reflecting surface of a reflecting member located in the lower side of the white board or the display unit, and the work has to be interrupted frequently in order to clean the reflecting surface to accurately detect a coordinate position Thus, in the conventional technology a load of cleaning the reflecting surface onto the user has been quite heavy.
Since the reflecting surface of a reflecting member is fixed to the white board, it is quite difficult to clean the surface, and especially the corners of the reflecting members on the two sides tend to accumulate the dirt therein and it is difficult to clean the dirt in these corners.
Further, the corners formed by the reflecting members on two sides have the smallest incident angle of a light beam from a light source, so that reflectivity of the light from the light source is reduced at these corners. When there are variations in joints each of two reflecting members at the corners, the reflectivity is further reduced.